Suction line accumulator

ABSTRACT

A refrigerant accumulator in the suction line of a closed refrigeration system, provided with a controllably heated metering tube between the bottom of the accumulator and a downstream point in the suction line, to ensure at least adequate re-evaporation of the refrigerant, to eliminate slugging and to return oil to the compressor, particularly during the hot gas defrosting portion of the refrigeration cycle, the heating being effected electrically or by means of hot gas from the compressor.

Unite States Patent 1191 Kramer 1 1 Feb. 11%, 197% [54] SUCTION LINEACCUMULATOR 2,701,455 2/1955 Kleist 62/503 X 3,071,935 1/1963Kapeker.... [75] Inventor Dame] Yardley 3,118,287 1/1964 Mocey 621196 x[73] Assignee: Kramer Trenton Company,

-Trenton, N.J Primary Examiner-Wi1liam F. ODea Assistant Examiner-PeterD. Ferguson [22] Flled' Sept 1971 Attorney, Agent, or FirmA1bert C.Nolte, Jr.; Ed- [21] A pl. N(),I 182,236 ward B. Hunter; C. BruceHamburg Related U.S. Application Data ABSTRACT [62] Division of Ser. No.858,749, Sept. 17, 1969, Pat.

160335367721 A refngerant accumulator 1n the suction lme of a closedrefrigeration system, provided with a controlla- 52 us. on. 62/503,62/278 hly heated metering tube hetweeh the bottom of the 51 1111. c1. 12511 43/110 accumulator and a downstream Point in the Suction 58 Field61 Search 62/196, 278, 503 10 ensure at least adequate re-evaporatioh ofthe refrigerant, to eliminate slugging and to return oil to [56]References Cited the compressor, particularly during the hot gas de-UNITED STATES PATENTS frosting portion of the refrigeration cycle, theheating being effected electrically or by means of hot gas from2,709,342 5/1955 Zearfoss, Jr. 62/503 X the compressor 2,783,621 3/1957Staebler et al..... 62/503 X g V 2,614,402 10/1952 2 (Ilaims, 9 DrawingFigures Swart 62/503 X PATENTEDFEB 1 9mm sum 1 ur 3 AccuMuLAToR R E V Ec E R PATENTEBFEBIQIQH 3.792.594

SHEET 2 0F -3 T0 CONDENSER PATENTEBFEBIQIHH 3792.594

' sum 3 or 3 6' FIG.7

EVAPORATOR CONDENSER I SUCTION LINE ACCUMULATOR This is a divisionalapplication of U.S. patent application Ser. No. 858,749 of DANIEL E.KRAMER, filed Sept. 17, 1969 and entitled REFRIGERATION SYS- TEM WITHSUCTION LINE ACCUMULATOR, which application has matured into US. Pat.No. 3,636,723, issued Jan. 25, 1972.

Modern positive displacement refrigerant compressor technology hasgenerated designs which provide the maximum in capacity per unit,weight, cost and power. In order to achieve these features thecompressors are generally designed for relatively high rotative speedsand high bearing loads. Standard rotative speeds for compressors are now1,725 and 3,400 revolutions per minute. At these speeds ingestion ofliquids of any sort into the compressor chamber can cause instantaneousmechanical failures. Liquid entering the cylinders can stem from twosources; liquid oil can enter the cylinders from foaming of the oil inthe compressor crankcase on start-up under conditions where liquidrefrigerant has condensed or dissolved in the oil during the off cycle.The other source of liquid is liquid refrigerant in relatively pure formwhich can return under abnormal conditions through the suction line fromthe evaporator.

If large quantities of liquid refrigerant enter the compressor, much ofthe refrigerant will be entrained into the cylinders with the vapor andwill cause a condition known as slugging which is accompanied bypounding and knocking sounds and frequently causes instantaneouscompressor damage.

If the liquid refrigerant returns to the compressor in small quantities,but over a long period of time, this liquid refrigerant tends to dilutethe oil, reducing its lubricity and generating a condition of rapidbearing wear under those designed conditions of high rotative speeds andhigh bearing loads to which the compressor is ordinarily exposed. Tohelp guard compressors against either immediate or long range damagecaused by the return of liquid refrigerant through the suction line tothe co mpressor, more and more compressor manufacturers are presentlyrecommending the use of so-called surge drums or suction accumulatorswhose purpose is to catch the liquid refrigerant returning in large orsmall quantities and prevent this potentially harmful liquid refrigerantfrom reaching the compressor. Because of the new requirements forsuction line protection against liquid return to the compressor, manymanufacturers have begun listing for sale suction accumulators withvarious refrigerant holding capacities and various inlet and outlet linesizes supposedly designed to fit a wide range of systems and refrigerantcharges.

Manufacturers of accumulators are faced with the problem of providingpositive means for the oil, which normally circulates with therefrigerant in refrigeration systems, to be returned to the compressor.If this oil is not returned but is caught or trapped in the suctionaccumulator, the compressor may run out of oil or the accumulatorspotential for holding liquid refrigerant will be diminished.

According to the present invention, there is provided an externalbleeder tube between the accumulator and the suction line together withone or more heaters so positioned, constructed, selected and controlledthat liquid refrigerant flowing through the bleeder tube is completelyre-evaporated before it reaches the suction line.

Practical embodiments of the invention are shown in the accompanyingdrawings, wherein:

FIG. 1 represents a vertical section of a known type of suction lineaccumulator;

FIG. 2 represents an elevation of another known type of accumulator,parts being broken away;

FIG. 3 is a diagrammatic view of a refrigerating system embodying theapparatus of the present invention;

FIG. 4 represents a vertical section of a first form of accumulatorembodying the invention;

FIG. 5 represents an elevation of a second form of ac cumulator;

FIG. 6 is a diagrammatic view of a portion of a refrigeration systemshowing an alternative means for heating the bleed tube;

FIG. 7 is a diagrammatic view of a refrigeration sys tem having meansfor heating both the bleed tube and the suction line;

FIG. 8 is a diagrammatic view of a portion of a refrigeration systemshowing the use of a thermostatic control for the bleed tube heater, and

FIG. 9 is a detail diagram showing means for ensuring discriminatingfunctioning of the thermostatic. control of FIG. 8.

According to FIG. I, the accumulator 10 is a vertically disposedcylinder having an inlet ill from the evaporator, opening at 12 into theupper part of the cylinder, and an outlet 13 leading to the compressor,the outlet being connected to a U-shaped trap 14 open at its free end 15to receive evaporated refrigerant and provided with a metering orificebleed hole 16 adjacent its bottom.

Since the bleed hole is built-in it must be made large enough to returnthe maximum flow of oil that might be expected. Unfortunately,experience has shown that if the bleed hole is made large enough toreturn the largest quantities of oil which mightbe pumped by anycompressor, the hole is then so large that excessive amounts ofrefrigerant are allowed to return to the compressor when the accumulatoris partially filled with liquid refrigerant. In addition, laboratorytests and experience have shown that the return of refrigerant and oilflow through the bleed hole is related to the vapor velocity passingthrough the accumulator. Although this effect would not at first appearto be obvious, the effect was positively determined by quantitativelaboratory tests. An investigation of the cause of this increase inrefrigerant flow through the bleed hole showed that it is caused by thepressure at the inside of the tube in which the bleed hole is locatedbeing much lower than the pressure on the outside. The pressure is lowerinside the tube not only by virtue of the frictional pressure drop lossin the outlet tube, but also the much greater pressure reduction causedby the Bernoulli effect, i.e., the higher the fluid velocity, the lowerthe pressure in that fluid.

All constructions of suction accumulators observed to this date areaffected by this problem which means that the rate of refrigerant flowfrom the body of liquid accumulated in the accumulator into the suctionline is not a constant but a variable.

An effort by the present applicant to solve this prob lem is shown inFIG. 2, wherein the horizontally disposed accumulator 17, having aninlet 18 and outlet 19 (corresponding to inlet Ill and outlet 13-15 inFIG. I)

is provided with an external bleeder tube 20, running from a point 21 atthe bottom of the accumulator to a point 22 in the suction line 19. Thisexternal bleeder tube 20 is so designed and constructed that it can beremoved and exchanged for a bleeder of a different diameter.

In addition, the easily serviceable design means that the bleed tube canbe more closely sized to the actual requirements without any concernthat dirt might plug the bleed tube and permanently destroy theusefulness of the accumulator.

Instead of the bleeder having to be made sufficiently large for theworst situation, the bleeder can be made with an internal borewhich'exactly matches the system requirement. Even if an error is madein initially sizing the bleeder its replacability makes a sizeadjustment an easy matter.

Even though the development of the suction accumulator with external andreplaceable bleed tube constituted a tremendous advancement over thebest previously available accumulators, and although the application ofthis accumulator has been satisfactory, all these accumulators hadcertain application limitations. All accumulators had, generally, to beinstalled so that a relatively long run of suction line existed betweenthe outlet of the accumulator and the compressor inlet. In addition, thesuction line had to be exposed to an ambient 32F or higher. The purposeof requiring this length of suction line is maintained at a relativelyhigh ambient was to insure that even the limited amount of liquidrefrigerant that flowedthrough the calibrated bleeder tube into thesuction line under conditions when floodback into the accumulatoroccurred, was completely evaporated to dryness so that no liquidrefrigerant at all entered the compressor. Under the conditions wherethe accumulator was placed very close to the compressor and/or where avery short suction line was employed, or the suction line was exposed tocold winter ambients, for example -F or F, reevaporation of even thesmall amount of liquid refrigerant bled through the bleeder tube couldnot occur and this liquid refrigerant entered the compressor causing oildilution and excessive bearing wear leading to early compressor failure.

In order to make sure that no liquid refrigerant returns to thecompressor, even where the suction line is short and cold as, forinstance, where the accumulator is mounted directly on the compressorchassis, either of two solutions can be employed. A first possiblesolution is the provision of a heat exchanger in the suction linebetween the accumulator outlet and the compressor using, for instance,the heat available from the hot gas leaving the compressor discharge towarm the suction vapor leaving the accumulator and evaporate the liquidmixed with that vapor. This system has the drawback that the normallycold suction vapor is heated not only when the ambient surrounding thesystem is low, as in the winter, but also when the weather is very hot.Then the suction heat exchanger aggravates potential compressoroverheating and reduces compressor capacity by warming the suction vaporentering the compressor which makes the vapor less dense and allows thecompressor to pump less with'each rotation of its crankshaft.

As illustrated in FIG. 3, a refrigeration system in which the presentinvention may be embodied includes the evaporator supplied with liquidrefrigerantfrom the condenser 31 and receiver 32 under the control ofthe expansion valve 33. The compressor 34 supplies gaseous refrigerantunder compression through the line 35 to the condenser, duringrefrigeration, or through the hot gas defrosting line 36, controlled bysolenoid valve 37, directly to the evaporator 30 during defrostmg.

The accumulator 38 is similar to that shown in FIG. 2, receivingrefrigerant from the evaporator through the line 39 and having an outlet40 opening into the upper part of the accumulatorand connecting with thesuction line 41 to the compressor. An external bleeder tube 42, similarto tube 20, leads from the bottom of the accumulator to the suction lineand there is also provided, according to the invention, a heater 43 sopositioned and controlled that liquid refrigerant flowing through thebleed tube is completely reevaporated before it reaches the suctionline. This construction has the advantage that even strong heating ofthe bleed tube will have essentially no effect on the temperature of thevapor entering the compressor. The heater therefore becomesdiscriminating in that it only heats liquid refrigerant or perhaps oilleaving the accumulator via the bleed tube but does not exert anyheating effect on the suction vapor transversing the accumulator itself.

Such an accumulator, with heated bleed tube, can be mounted at or nearthe compressor, will allow free return of oil which is trapped in theaccumulator, and yet effects the complete evaporation of liquidrefrigerant traversing the oil flow passage without any heating effecton the suction vapor entering the compressor. This system can be usedfor defrosting of evaporators even when the compressor, accumulator andother high side components are located in ambients as low as 0 F or 10F.

An additional improvement in accumulator design is a modification, shownin FIG. 4, which at least partially offsets the variation in refrigerantflow through the bleeder which occurs with various vapor velocities.This improvement constitutes extending the outlet of the bleed tube 44into the outlet tube 45 and bending this outlet, as indicated at 46,upwards so that a pilot tube effect is generated. With this constructionthe impact pressure of the vapor on the end of the bleed tube opposesthe increased pressure difference which higher vapor velocities,generate.

An additional refinement in the design of the bleed tube involves theapplication of heat in such a way as to sharply decrease the rate offlow which occurs through the bleed tube even when the bleed tube is ofa large diameter. FIGS. 3 and 4 show the basic bleed tube arrangement ofthis invention which pitches uniformly from the bottom of theaccumulator to the outlet tube with or without the pilot effect.

FIG. 5 shows the bleed tube 47 at one end thereof removably andinterchangeably connected to the bottom of accumulator tank 40, by tubeconnector fitting 47A, and similarly connected, at the other end of thetube, to the tank outlet tube 45 by connector 4713. The figure alsoshows the tube modified in the form of a trap 48. Heat is applied at 49on the downward flowing side of the trap and separately at 50 on theupward flowing side of the trap. The application of heat on the downwardflowing side of the trap generates bubbles whose buoyancy tends tooffset the pressure differential generated by the vapor flow and by thethe head of liquid in the accumulator. By the correct application of theheat at this point the flow of liquid refrigerant in the bleed tube canbe adjusted as required so that the heater 50 on the outward upflowingleg of the bleed tube can completely evaporate the liquid refrigerantwhich succeeds in traversing the downfiowing leg. Together the divisionof heat between the downflowing leg and the upfiowing leg constitutesmeans for externally changing the effective flow capacity of the bleedtube without actually modifying its internal construction or diameter byan interchange of tubes with the aid of the fittings 47A, 47B.

The bubbling of therefrigerant in the trap is comparable to the vaporlock effect obtainable in any small tube, including the tube 44 in FIG.4. When liquid refrigerant moves through a relatively small tube in theform of a solid column of liquid under a given head the flow of thatliquid is sharply impeded when the stream is heated and thereby assumesthe quality of a mixture of vapor bubbles plus liquid. This impedimentcaused by vapor bubbles in a refrigerant liquid stream moving in a smallbore tube is called vapor lock, and when an adequate amount of heat isapplied to the metering tube it could practically cut off most of theflow of liquid through it. While the application of heat to the meteringtube creates the condition called vapor lock in a refrigerant liquidstream, the application of heat to the metering tube while oil is movingthrough it during normal operation has practically a zero effect on theflow of the oil returning to the compressor during normal operationexcept that the oil becomes warmer and correspondingly less viscous.

Heating of the bleeder tube, as described above, is of particularimportance during defrosting, when some of the refrigerant from theevaporator is most likely to be in liquid form. However, the heaters 43,49, 50 may be kept on continuously, if desired, in order to avoid thenecessity for providing special controls. A suitable setting can bedetermined for any given installation and adjustments, if any, may thenbe on a seasonal basis. During normal operation of the system, forrefrigeration, with little or no liquid entering the accumulator, theheating of the small amounts of vapor passing through the bleeder tubehas a negligible effect on the refrigerant gas flowing to thecompressor, but whenever any liquid does enter the accumulator duringdefrosting or for any reason during refrigeration it is renderedharmless by the use of this invention.

As a practical alternative, heat from the compressor discharge may beused to ensure vaporizing temperatures in the bleed tube. FIG. 6 showsan arrangement in which the accumulator 51 has an outlet 52communicating with the suction line 53 to the compressor 54. The bleedtube 55 (similar to the tubes 42 or 44) is heated by close associationwith the line 56 through which flows a portion of the hot gas which isby-passed around a throttling device 58 in the discharge line 57.

The line 56 and tube 55 may be strapped or soldered together to ensureheat transfer contact. All parts of the suction line normally tend, withvarying degrees of effectiveness, to vaporize liquid refrigerant passingtherethrough. if the distance from the evaporator to the compressor orfrom the accumulator to the compressor is short, there would be moreneed for heat in the bleed tube and/or in the suction line than therewould if such distances were longer. Since the discharge line carriesmuch more heat than is needed for ensuring complete vaporization in thesuction line, the line 56 in FIG. 6

may be relatively small and the throttling device 58 may be either ahand valve, for adjustment as required,

or an orifice of selected size, to ensure an adequate diversion of hotgas through the line 56, while permitting most of said gas to followitsnormal course to the condenser.

If the refrigeration system includes provision for hot gas defrosting,the hot gas line can be routed adjacent to the suction line, as shown inFIG. 7, where the accumulator 59 with inlet 60, outlet 61 and bleed tube62 is associated with hot gas lines for heating both the bleed tube andthe suction line 63. The compressor discharge line 64 includes a portion65 in heat transfer contact with the bleed tube 62 (as in FlG. 6) whilethe hot gas defrost linefi, controlled by solenoid valve 67, issimilarly in heat exchange relation to the suction line 63 throughout asufficient length of said outlet line for the accumulator, to evaporateliquid returning during defrost. This supplementary heating wouldprovide a safety factor in case of excess liquid return from theevaporator to the accumulator, above the vaporizing capacity of themetering tube. Such heating of the suction line would not have theharmful effects of continuous heating, mentioned above, since theheating takes place only during defrosting and the suction line is notheated during normal refrigeration.

Where electric heaters are used they may be arranged to turn on when thecompressor starts and to turn off when the compressor stops, as by meansof a relay indicated conventionally at 70, in FIG. 3, associated withthe compressor motor circuit. If consumption of electric power must becontrolled carefully a thermostat may be provided on the suction linenear the compressor inlet to turn on the heater or heaters when thesuction line becomes cold, implying the presence of liquid refrigerant.This would mean that electric heaters might remain de-energized for longperiods of time, for instance, during warm weather when the accumulator,bleed tube and suction line cooperate inherently to perform theirrte-evaporating function. In colder weather, however, when the ambientaround the suction line is such that liquid flowing through the bleedtube is not re-evaporated, the heater would be turned on. a i

In FIG. 8 is shown a portion of a system similar to thatof FIG. 3 buthaving thermostat 711, with bulb 72 adjacent suction line 73 arranged toopen and close the switch 74 in the circuit of heater 75 (correspondingto heater 41-3).

The use of a thermostat detecting only the suction line temperature, asa means for ascertaining the presence or absence of liquid, is notalways reliable since liquid refrigerant at a temperature higher thanthe thermostat setting could, under certain circumstances, be presentand could return to the compressor without de tection by the thermostat.As an added refrinement, to eliminate the possibility just mentioned, asmall cartridge heater 76 (FIG. 9) may be added to the suction line 77adjacent the thermostat bullb 78, or to said bulb itself, in order toensure that the thermostat will react only to the presence of liquid,assuming a setting higher than the temperature of any returning liquid.The cooling ability of liquid refrigerant is about times better thanthat of vapor refrigerant. With liquid refrigerant in the suction lineof the bulb of the thermostat is effectively cooled despite the presenceof the small heater 76, tripping the thermostat and energizing therelatively high voltage heater on the bleed tube. If there is only coldvapor in the line, its cooling effectiveness is insufficient to overcomethe heating of the bulb by the heater 76 and the bleed tube heater isnot energized. The arrangement just described constitutes a positivemeans for detecting the presence of liquid refrigerant in the suctionline without putting a sensor directly in the flow stream.

What is claimed is:

1. An accumulator for a refrigeration system comprising a tank, an inletconnection, an outlet connection extending below the tank, a conduitmechanically coupled to the bottom of the tank and the outlet conection,extending only underneath the tank, constituting a trap which has afirst leg, descending from the tank,

stream.

1. An accumulator for a refrigeration system comprising a tank, an inlet connection, an outlet connection extending below the tank, a conduit mechanically coupled to the bottom of the tank and the outlet connection, extending only underneath the tank, constituting a trap which has a first leg, descending from the tank, a second leg rising to the outlet connection, heating means thermally connected to said first leg, and separated heating means thermally connected to said second leg.
 2. An accumulator for a refrigeration system comprising a tank, an inlet connection, an outlet connection extending below the tank, a conduit mechanically coupled to the bottom of the tank and said outlet connection and extending only underneath said tank, and a heater thermally connected to said conduit, the outlet of the said conduit extending into said outlet connection and being provided with an opening facing upstream. 